1. Field of the Invention
The present invention generally relates to soil remediation systems and methods. More particularly embodiments of the present invention relate to systems and method for In-Pile Thermal Desorption (IPTD) in a wall and/or floor heated chamber.
2. Description of Related Art
Soil contamination is a matter of concern in many locations. “Soil” refers to unconsolidated and consolidated material in the ground, and to sediment in water bodies such as rivers, harbors and estuaries. Soil may include natural formation material such as dirt, sand, and rock, as well as fill material. Soil may be contaminated with chemical, biological, and/or radioactive compounds. Dealing with these types of contaminants of concern (COCs) so as to protect human health and the environment represents a challenge to modern society.
There are many ways to remediate contaminated soil. “Remediating soil” means treating the soil to reduce contaminant levels or mobility within the soil or to remove contaminants from the soil. Ex situ methods of remediating contaminated soil typically include excavating the soil and then processing the soil in an on-site or off-site treatment facility to reduce contaminant levels within the soil or to remove contaminants from the soil. Alternatively, contaminated soil may not be excavated but instead remediated in place, which is termed “in situ remediation”.
During remediation heat added to contaminated soil may raise the temperature of the soil above vaporization temperatures of soil contaminants. If the soil temperature exceeds a vaporization temperature of a soil contaminant, some or all of the contaminant will vaporize. Thermal desorption is a soil remediation process that involves in situ or ex situ heating of contaminated soil. Heating the soil may reduce soil contamination by processes including, but not limited to, vaporization and vapor transport of contaminants from the soil (e.g., steam distillation), entrainment and removal of contaminants in water vapor and/or a gas stream, thermal degradation (e.g., by pyrolysis and/or hydrolysis), and/or conversion of contaminants into other compounds by oxidation or other chemical reactions within the soil. During thermal remediation, a vacuum may be applied to the soil to remove off-gas and/or other fluids from the soil. The off-gas and other fluids may be directed to a storage tank or treatment facility and processed to remove contaminants from the extracted fluids or to reduce contaminant levels within the fluids.
Soil may be heated by a variety of methods, both in situ and ex situ. Methods for heating soil include, but are not limited to, heating by direct firing, convection (e.g., rotary kiln), heating substantially by thermal conduction, heating by steam injection, heating by radio frequency heating, or heating by electrical soil resistivity heating. Thermal conductive heating (“TCH”) may be advantageous because the temperature obtainable by thermal conductive heating is not dependent on an amount of water or other polar substance in the soil. Soil temperatures substantially above the boiling point of water may be obtained using thermal conductive heating, if needed. Soil temperatures of about 100° C., 200° C., 300° C., 400° C., 500° C. or greater may be obtained using thermal conductive heating. By achieving such temperatures, a very wide range of organic contaminants and some metals (e.g., mercury) can be treated and substantially if not completely removed from the soil.
Increasingly, excavation and offsite disposal of these contaminants, which involves transferring the contamination to another location, such as a landfill, is regarded as too costly and detrimental from a liability standpoint. In-Pile Thermal Desorption (IPTD) is an emerging technology that treats contaminated soil, sediment or other material in batches. Soil piles or treatment cells are typically built with heaters or heat pipes installed within the soil volume, after which the piles or cells are covered. The piles or cells are then heated to the target temperature, and when the goals have been reached, the treated soil is removed as the heating system is dismantled and moved out of the way. Completing a full cycle of this process typically takes less than two months. IPTD can be carried out onsite and is relatively insensitive to the presence in the waste of high moisture and organic contents, fine particles, and rocks or debris.
U.S. Patent Publication 2004/0228690 by Stegemeier et al., U.S. Pat. No. 6,881,009 by Stegemeier et al., U.S. Pat. No. 7,004,678 by Stegemeier et al., and U.S. Pat. No. 7,534,926 by Stegemeier et al., the entirety of each is herein incorporated by reference as if fully set forth herein, describes systems and methods for heating contaminated soil.
Current IPTD techniques may include certain difficulties and challenges, such as installing or removing the heating system and gas inlet/vacuum piping inside the soil volume without later damaging them, readily accessing an interior of the cell with a soil loading vehicle, such as a bulldozer or dump truck used to deposit and/or remove the soil without first dismantling each heater or assembly of heaters. Other treatment techniques that include heating the soil through injection of a fluid such as hot gas can result in uneven heating due to preferential flow of the hot gas through higher permeability pathways (e.g., sandy seams, fractures between silty/clayey blocks or aggregates, voids), and bypassing of lower permeability zones, exemplified by silty/clayey blocks or aggregates.